Clooney's Obama fundraiser is expected to raise $15 million, mostly from general public donations for a chance to attend. It comes as fundraising changes.

"The campaign is heating up," said Ken Solomon, co-chairman of the Obama campaign's finance committee for Southern California. "This is the first event where we really have the clear face of the competition. You've got an energized base in that the election is really on and we know who it is we're running against. Plus, it's George Clooney's house. Clearly that has something to do with it."

Fundraising events similar in size and intimacy to the Clooney party typically raise between $1 million and $4 million. Whether Obama will use similar online contests to replicate the success of the Clooney dinner with other celebrity supporters and hosts remains to be seen. But Ross predicted that as the president attempts to draw a wider swath of the public to the polls, including young voters, entertainment shows and personalities will become an increasingly crucial part of his campaign.

"Entertainment is gonna become part of the protein of the campaign, not just the dessert," he said.

As much as the Clooney event is expected to draw, its haul could be dwarfed by the unlimited donations flowing to so-called super PACs, the product of several federal court rulings, including the Supreme Court's 2010 decision in the Citizens United case. Talk show host Bill Maher, who gave $1 million to the pro-Obama super PAC Priorities USA Action, is not attending the Clooney fundraiser.

"Ironically, that's the chump change in this election," Maher said of events like the $40,000-a-plate Clooney dinner. "That's not where this country has moved. This is a fairly new atmosphere we live in with Citizens United. Most of the rich donors are Republicans. I was trying to make the point that if you want to even the playing field, the people who have money on the left really have to get in the game. And most of them are here in California."

Katzenberg has contributed more than $2 million to Priorities USA himself — "sometimes you must actually fight fire with fire," he said — but he views a fundraiser like the Clooney event as more valuable in the long run because it's transparent and reflects the support of a wider cross-section of donors.

"Every dollar that is given legitimately through national campaigns, through proper legal channels, is worth five times or 10 times every dollar that's given through PACs," he said.